Command to increase font size and spreading in steps

Question

I have been having trouble with this for some time by now. I want a command \relfontsize{<fontstep>}{<spreadstep>} that works exactly like \fontsize{<fontsize>}{<spreadsize>}, except that it works relatively: It multiplies the font size by 1.20^(<fontstep>) and the line spreading by 1.20^(<fontspread>). So what happens is

fontsize    ---> (1.20)^(<fontstep>)   *   oldfontsize
linespread  ---> (1.20)^(<spreadstep>) *   oldlinespread

(here <fontstep> and <spreadstep> are integers, which may take negative values)

I have <fontstep> more or less working (using this other question of mine), but <spreadstep> causes trouble.

(I do not know if this is going to matter, but I am compiling my document using LuaLaTeX.)

\documentclass[10pt]{memoir}

% Commands that allow me to use powers in \dimexpr expressions:
\usepackage{expl3}
\ExplSyntaxOn
\cs_new_eq:NN \fpeval \fp_eval:n
\cs_new_eq:NN \fptodim \fp_to_dim:n 
\ExplSyntaxOff

\makeatletter
\def\getcurrentfontsize{\f@size pt}
\makeatother

\newcommand*\relfontsize[2]{
\fontsize{\dimexpr\fpeval{1.2^(#1)}\dimexpr \getcurrentfontsize\relax}{%
        %please do some magic for me
   }\selectfont%
}

\begin{document}

First paragraph, normal size.

{

\relfontsize{1}{2} Let's increase the font size by 20 percent and the line spreading 
by 20 percent two times (that is, by 44 percent), BOTH numbers relative to the first paragraph.

\relfontsize{1}{1} Let's increase both further by 20 percent compared to the last paragraph

}

Now we're back at the old size.

\end{document}

The question is perhaps a bit difficult to explain, so if anything at all does not make sense, don't hesitate to comment, and I shall do my best to explain! :-) — Gaussler, Jan 22 '15 at 18:23
Yes, I feared that sentence would cause confusion. "Increase x by y n times" means (to me) to change x to x y^n. Because I multiply x by y, and I do it n times. — Gaussler, Jan 22 '15 at 18:28
I know it's confusing, but I cannot think of another formulation. But feel free to suggest one. — Gaussler, Jan 22 '15 at 18:30
If you had specified luatex in your earlier powers question it would have been easier, lua has exponentiation:-) — David Carlisle, Jan 22 '15 at 18:46

Werner · Accepted Answer · 2015-01-22T19:12:08.010

Once you set the \fontsize, you need to \selectfont. The following minimal example implements what you're after with the addition of the <baseline> component - stored in \f@baselineskip:

enter image description here

\documentclass[10pt]{memoir}

% Commands that allow me to use powers in \dimexpr expressions:
\usepackage{expl3}
\ExplSyntaxOn
  \cs_new_eq:NN \fpeval \fp_eval:n
\ExplSyntaxOff

\makeatletter
\newcommand{\getcurrentfontsize}{\f@size pt}
\newcommand{\getcurrentbaseline}{\f@baselineskip pt}
\makeatother

\newcommand*\relfontsize[2]{%
  \fontsize
    {\dimexpr\fpeval{1.2^(#1)}\dimexpr\getcurrentfontsize\relax}
    {\dimexpr\fpeval{1.2^(#2)}\dimexpr\getcurrentbaseline\relax}%
  \selectfont%
}

\begin{document}

First paragraph, normal size.

{%
\relfontsize{1}{2} Let's increase the font size by 20 percent and the line spreading 
by 20 percent two times (that is, by 44 percent), BOTH numbers relative to the first paragraph.

\relfontsize{1}{1} Let's increase both further by 20 percent compared to the last paragraph.\par
}

Now we're back at the old size.

\end{document}

Note that it is important to issue a paragraph break (either implicitly via an empty line or explicitly via \par) in order to produce the appropriate baseline skip for the font change. I've used both above.

Command to increase font size and spreading in steps

1 Answers1